As known as “ad-hoc network”, a system is considered in which a plurality of users in a certain range form a wireless network with wireless terminals carried by these users and transmit messages (or mail message) and music data, for example, to each other, thereby implementing communication among the users.
Referring to FIG. 15, there is shown an outline of this wireless network system. A terminal 1x is carried by user X, a terminal 1a is carried by user A, a terminal 1b is carried by user B, a terminal 1c is carried by user C, and terminal 1d is carried by user D, each being a wireless terminal. The terminals 1a, 1b, and 1c are located in an area 4 enclosed by a circular boundary 3 with the terminal 1x at the center thereof. The terminal ld is located outside the boundary 3.
The boundary 3 is located farthest from the terminal 1x, for example, from which radio wave reaches for wireless communication. Namely, any terminal of which distance from the terminal 1x is below predetermined distance Dx can communicate with the terminal 1x. 
Therefore, in the example shown in FIG. 15, users A, B, and C of the terminals 1a, 1b, and 1c, respectively, are displayed as in-service-area user on a display screen 2x of the terminal 1x, in the nicknames attached to the terminals, as shown in the bottom of the figure.
User x of the terminal 1x can select a mate of chat, for example, from among the users in the service area to communicate with the selected mate, such as transmitting messages to the selected user, exchanging messages with the selected mate, transmitting music data recorded to the terminal 1x to the selected mate, and receiving music data recorded to the terminal of the selected mate, for example.
Patent Document 1 (Japanese Patent Laid-open No. 2004-135086) below discloses a method of getting the positional information of a mobile wireless terminal in a communications system having a base station wirelessly communicable with a mobile wireless terminal without requiring a dedicated server or a dedicated line.
Patent Document 2 (Japanese Patent Laid-open No. 2003-219453) discloses a method of managing the location of each user while protecting the privacy of each user in a location management system made up of a server and wireless terminals carried by users, which is installed in an office, for example.
However, in the above-mentioned related-art method shown in FIG. 15, a display screen 2x of the terminal 1x shows all of users A, B, and C as in-service-area users who are communicable inside a communicable area 4. Hence, if user X selects user B to execute chat between user X and user B, for example, and, if user B is in the proximity of user X, in front of user X, for example, the locations user X and user B can be found out by each other.
The above-mentioned prior-art technical documents are as follows:
Japanese Patent Laid-open No. 2004-135086
Japanese Patent Laid-open No. 2003-219453